So if long-standing opponents of the EU are starting to sound a little tedious in their denunciations of “the Guilty Men” who tried to push Britain into the euro, forgive us. But when the entire political class of our continent has got such an important issue so utterly wrong it’s not something that should be brushed aside.

And when the establishment has been so exposed, it is rational that we start to question its other orthodoxies. James Delingpole and Guido Fawkes, among others, see parallels with the political consensus over climate change, and indeed Peter Oborne’s description of the appeasement era, “when dissent was greeted with suffocating ostracism and personal calumny, reminiscent of the fate of religious non-conformists in earlier times” could be applied to many areas where the British elite become ferocious towards bad-thinkers. This Independent editorial from 1992 will be studied in history books for years to come, as an example of politically motivated hate. (And, I hope, in psychiatrists’ manuals.) Yet the European project – the euro delusion – is part of a wider utopian mania that grips the political class.

At the Labour Party conference two days ago, Ed Miliband said that Labour had got it wrong over immigration, and “underestimated the level of immigration” from Poland. Only by a factor of 100 to 1 – so don’t worry about it. However, as my colleague Philip Johnston points out, this is to give a totally misleading account of Labour’s immigration policy, of which the A8 migration was just one part.

And it was not just that Labour “got it wrong” in a technical sense. They were systematically, fundamentally wrong in their entire philosophy, a level of wrong-ness that only comes about when intelligent people suffer from collective madness. Their approach to immigration, as many party workers have since confessed, came about from a flawed belief that ethnic, religious and cultural diversity was itself a good and liberal thing, a millennial belief in a universalism that could be called the diversity delusion.

The diversity delusion and the euro delusion are both symptoms of a similar pseudo-religious mania. Both sprung from a noble attempt to ensure that the horrors of 1914-1945, inspired by nationalism and scientific racism, were never repeated. Both make them more likely to be repeated. Jean Monnet, architect and first president of the European Coal and Steel Community, conceived the idea of a United States of Europe in order to ensure such wars never happened again, through a new empire in which nationalism had been erased. Because Monnet was opposed by Charles de Gaulle, who favoured a Europe of nations, he therefore he developed the “Monnet method” of “integration by stealth”, a policy that ultimately led to the tragedy of economic union.

Perhaps more influential still was Alexandre Kojeve, who set up the embryonic European Union and influenced a generation of pro-EU thinkers in France. He came up with the “end of history” theme, whereby national boundaries and exclusive communities would wash away and a new world without borders would emerge. The EU’s vapid motto, United in diversity, reflects this neo-Christian utopianism.

Without exception the guilty men of Europe also shared, and still, share, the diversity delusion. The Liberal Democrats have entirely signed up, and most of the Labour Party too, although the Tories must share the blame too. Only one senior Tory spoke up against both mass immigration and the Common Market, Enoch Powell (who was also a voice in the wilderness in opposing Keynesian policies – only Paul the Octopus in recent years has been more right). Powell’s provocative language certainly helped his opponents, but as immigration is by its very nature a more toxic subject, so milder opponents have been silenced, leaving only the cranks, oddballs and extremists to represent opposition to this new utopia. This in turn makes it easier to present critics as extremists, just as even a couple of years ago opponents of the euro were labeled extremists and xenophobes. Contrary to what proponents of this delusion claim, it is not about xenophobia or racism; the issue, as Charles Moore wrote on Saturday, is one of sovereignty, and sovereignty relies on the legitimacy that only nations can provide.

Instead, as Roger Scruton noted, European intellectuals tried to “discard national loyalty and to replace it with the cosmopolitan ideals of the Enlightenment… The problem… is that cosmopolitan ideals are the property of an elite and will never be shared by the mass of human kind.”

The European project was a utopian idea, and I suspect that Britain’s peripheral part in the third great stupid, European idea of the last century will soon be over. National loyalty, whatever the elites feel, is here to stay. I guess we’re all extremists now.